v14_amit_2.patch.txt

diff --git a/src/backend/replication/logical/worker.c b/src/backend/replication/logical/worker.c
index 06ba6d3a64..e89e811c51 100644
--- a/src/backend/replication/logical/worker.c
+++ b/src/backend/replication/logical/worker.c
@@ -4135,6 +4135,7 @@ get_candidate_xid(RetainConflictInfoData *data)
 	data->last_phase_at = InvalidFullTransactionId;
 	data->phase = RCI_REQUEST_PUBLISHER_STATUS;
 
+	/* process the next phase */
 	maybe_advance_nonremovable_xid(data);
 }
 
@@ -4156,6 +4157,10 @@ request_publisher_status(RetainConflictInfoData *data)
 	else
 		resetStringInfo(request_message);
 
+	/*
+	 * We send the current time to update the remote walsender's latest reply
+	 * message received time.
+	 */
 	pq_sendbyte(request_message, 'S');
 	pq_sendint64(request_message, GetCurrentTimestamp());
 
@@ -4213,6 +4218,7 @@ wait_for_publisher_status(RetainConflictInfoData *data)
 	else
 		data->phase = RCI_REQUEST_PUBLISHER_STATUS;
 
+	/* process the next phase */
 	maybe_advance_nonremovable_xid(data);
 }
 
@@ -4226,8 +4232,10 @@ wait_for_local_flush(RetainConflictInfoData *data)
 		   FullTransactionIdIsValid(data->candidate_xid));
 
 	/*
-	 * Issue a warning if there is a detected clock skew between the publisher
-	 * and subscriber.
+	 * We expect the publisher and subscriber clocks to be in sync using
+	 * time sync service like NTP. Otherwise, we will advance this worker's
+	 * oldest_nonremovable_xid prematurely, leading to the removal of rows
+	 * required to detect update_delete conflict.
 	 *
 	 * XXX Consider waiting for the publisher's clock to catch up with the
 	 * subscriber's before proceeding to the next phase.
@@ -4235,7 +4243,7 @@ wait_for_local_flush(RetainConflictInfoData *data)
 	if (TimestampDifferenceExceeds(data->reply_time,
 								   data->candidate_xid_time, 0))
 		ereport(WARNING,
-				errmsg("non-removable transaction ID may be advanced prematurely"),
+				errmsg("oldest_nonremovable_xid transaction ID may be advanced prematurely"),
 				errdetail("The clock on the publisher is behind that of the subscriber."));
 
 	/*
@@ -4276,6 +4284,7 @@ wait_for_local_flush(RetainConflictInfoData *data)
 
 	data->phase = RCI_GET_CANDIDATE_XID;
 
+	/* process the next phase */
 	maybe_advance_nonremovable_xid(data);
 }